Method for delaminating sized laminar mineral particles



Dec. 22, 1964 M. l. COHN ET AL METHOD FOR DELAMINATING SIZED LAMINAR MINERAL PARTIGLES Original Filed Dec. 22, 1958 4 Sheds-Sheet 1 GARNET a MIGA WATER SLURRY PRESSURE mfiglRgggfl L CONGENTRATOR FEED TANK 6gp PUMP a VALVE K GRAVITY 2 3 4 FEE /2 x D 32 Q PRESSURE i cRusHER PUMP a VALVE LORE scREEN OENTRIFUGE DR DEAGGLOMERATOR DRYER GLASSIFIER FINISHED PRoDuc'r F l G.

GARNET 8 mm WATER SLURRY PRESSURE fig rgg CONCENTRATOR FEED TANK pggp Pumps VALVE GRAVITY K 3 FEED 34 ovERs|zE REGYGLE SCREEN cRusHE CLASSIFIER ORE 'gggfi DEAGGLOMERATOR DRYER CENTRIFUGE F l G. 2

INVENTORS MORRIS I. OOHN ROY D. PERDUE BY m m anamm ATTORNEYS Dec. 22, 1964 M. l. COHN ETAL 3,162,379

METHOD FOR DELAMINATING SIZED LAMINAR MINERAL PARTICLES Original Filed Dec. 22', 1958 4 Sheets-Sheet 2 INVENTORS MORRIS I. COHN ROY D. PERDUE ATTORNEYS 1964 I M. I. COHN ETAL 3, 62,379

M F DELAMINATING SIZED M T IN V EN TORS BY wsY 'a 22%;

031/52, fiammyflmm ATTORNEYS Dec. 22, 1964 M. COHN ETAL 3,162,379

METHOD FOR DELAMINATING SIZED LAMINAR MINERAL PARTICLES Original Filed Dec. 22, 1958 4 Sheets-Sheet 4 i Q Q Q Q \D Q Q \\p kQ- ba Gk a v m \J a" r? Q n g;

w 9 m w T (1 kg m (Ra F IQ L\ 1&-

YQ INVENTORS MORRIS l. COHN BY ROY D. PERDUE ,81%a,%0779ad0l6/Z0m ATTORNEYS United States Patent 3,162,379 METHOD FUR DELAMRNATKNG SHZED LAMENAR I /HNERAL PARTEQLES Morris H. Colin, Needham, and Roy B. Pcrdue, Ten/ksbury, Mass, assignors to Mineral industries Corporation of America, Needharn, l t lass, a corporation of Massachusetts (Iontinuation of applications Ser. Nos. 197,812 and 197,813, May 17, 1962; said application Ser. No. 197,813 being a continuation of application Ser. No. 189,933, Apr. 24, 1962, which is a continuation of application Qer. No. 782,992, Dec. 22, 1958. This application (Pct. 14, 1963, Ser. No. 316,1ti7

13 Claims. (Cl. 24l4) The present invention relates to a method of any apparatus for grinding and delaminating mica, especially mica derived from mica schist ores.

Mica is found in nature in the form of schist, pegmatite, alaski-te and other deposits. Some schist deposits contain as much as 60% or higher mica by weight. Pegmatite ores, now being commercially worked, seldom yield higher than mica from the total rock mined. The former are soft, consist of small particles of mica dispersed throughout the rock and are easily worked by open pit mining techniques. The latter occur in hard rock as veins and are inherently more d-ifficult to mine. Schist deposits therefore are attractive sources of mica if the delaminated ground product derived therefrom could meet the specifications of the mica consuming industries. However, prior to the present invention, no commercially successful method has been found to grind schist mica to obtain a mica product which is acceptable commercially in spite of the fact that many attempts have been made to do so.

Mica occurs in nature as clusters of laminated sheets called blocks or books. In schist, these books are quite small, perhaps to /s inch across and smaller and are dispersed throughout the rock. On the other hand, mica books from conventional pegmatite veins may run several inches in one or more dimensions. Mica derived from pegmatite deposits can be delaminated and ground by several well known Wet and dry processes to yield fine particles having a plate-like structure. It is this platelike or flaky shape that mainly accounts for the utility of ground mica. Mica derived from alaskite deposits (in the mining of feldspar) also lends itself to conventional delaminating and grinding techniques yielding fine flakes. On the other hand, sclu'st mica and mica from other sources containing a large percentage of fines have always been difficult to delaminate and grind to sufficient fineness while still preserving a plate-like particle shape. In other words, it is difiicult to delaminate the small books of mica in schist and other mica products containing the same and reduce the delaminated sheets to flakes of proper fineness without destroying the plate-like struc ture of the mica. With most conventional grinding techniques, the ground particles obtained from schist mica and other mica containing a large percentage of fines are not sufliciently flaky and consequently the resulting prodnot is commercially unsatisfactory. It is believed that the reason for this is that the small books are ground as such into smaller books without delamination occurring.

The paint industry, wallboard-joint cement manufacturers, and other high tonnage consumers or" ground mica have established particle size and bulk density specifications, among others, in order to control the quality of the mica being used in their products. It has been found that the bulk density, i.e. the actual weight of ground mica contained in a given flutfed or riflled volume thereof (pounds per cubic foot), correlates Well with the fiakiness and fineness of the individual particles. The more flakes present in a sample, i.e. the greater the degree of delamination, the greater the percentage of voids and thus the lower the bulk density. The lower the bulk density and the finer the flakes, the higher the quality of the product. The bulk densities of undelaminated mica ground and unground and of ground mica, the plate-like shape of which has been destroyed, are relatively high.

The best and more costly ground mica products obtained from dry and wet grinding methods have bulk densities of 10 to 14 lbs. per cubic foot. Of these products, the finer grinds having particles of dimensions less than 44 microns (minus 325 mesh) command the higher selling prices.

No commercially satisfactory, instantaneous and continuous method of grinding a true schist mica and other mica products containing a large percentage of fines to low bulk densities 1014 pounds per cubic foot and lower) and fine particle size has been known prior to this invention. Batch type Wet mulling as practiced in water ground mica manufacture will delaminate schist mica, but this method is unattractive because of the long time cycles and high overall cost.

An object of the present invention is to provide for the first time an economical, commercially feasible, instantaneous and continuous method of delaminating and grinding schist mica and other mica products containing a high percentage of fines into fine, flaky particles without destroying the plate-like structure of the mica, to produce a fine, flaky mica product having a sufficiently low bulk density and suflicient flakiness and fineness to meet the most exacting standards of the mica consuming industries. While primarily designed for schist mica, the delaminating and grinding method of the present invention provides an economical, instantaneous and continuous method for grinding conventional scrap or book mica derived from pegmatite, alaskite and other mica deposits or from mica trimmings and splittings to the necessary particle size and bulk density specifications required for the more costly ground mica products.

A further object of this invention is to provide a commercially feasible, economical, instantaneous and continuous method of delaminating and grinding mica, which in addition to having the advantages above referred to, can accommodate, as feed, mica books of fine size which heretofore had to be discarded.

A still further object is to provide an improved method of delann'nating and grinding mica.

A still further object is to provide an apparatus for carrying out the above-mentioned method.

The method of the present invention comprises applying a high fluid pressure on a liquid slurry of mica books or blocks to force it to flow at a high velocity through a highly-restricted opening in the nature of a fraction of an inch formed by closely spaced hard surfaces designed to impart shearing, turbulence, shattering, impact, and cavita tion forces on the mica books to delaminate and grind them into fine flakes. The slurry is discharged from the opening at a high velocity against a hard impact surface directly in front of the opening. In a preferred embodiment, the restricted opening comprises a valve opening and the slurry under high pressure is directed against the valve to force it slightly away from its seat against the force of resilient means such as a spring or the like yieldingly urging it toward its seat, whereby the slurry under pressure is forcedat an extremely high velocity through the highly restricted opening between the valve and its seat and against the impact surface. The'direction of flow of the slurry through the valve opening is at an angle to the direction of flow to the valve, and the opening is preferably annular in shape. I

Preferably, the valve is rotated to prevent the slurry the ore normally require water.

iv the requirements'of thepriorfa'rtf A With reference to thedrawin'ga'fthe mica. ore," (schist,

from wearing a channel in the valve, seat and to. cause the wear efiectsof the slurry on the valve and valve seat to be more uniform whereby the useful life of the valve rand valveseat before overhaul and repair becomes necessary is substantially increased.

. The fluid pressure can be generated by a suitable pressure pump such as a piston pump operating onthe slurry. The valve, mounted on the pump discharge, can be any.

one of several designs such as that used for the-high pressure homogenizing of milk. a

The impac't'surface can be provided by an impact ring around the annular valve openingand. within a fraction of an inch therefrom, as is customary with valves of this design. The ring. forms with theoutside of the valve a I passage of restricted cross section extending at an angle to the valve opening and through which the slurry flows after impacting" against the ring.

- reagents, if necessary; The mica and water discharged from flotation unit 3 flowvto'the mica slurry feed tank 4 to which additional water is added'to obtain the desired concentration of mica in water.. The mica and waterare agitated'in tank 4 by-agitator's toproduce a'uniform aqueous rn'ica'slurry which. is fed by gravity or a pump to the inlet 7 of liquid piston pump 10 of the pressure pump and valve assembly 12. The slurry is sucked from inlet 7 through-suction ball-check valve 13 of pump 10 into the pump cylinder 14 by the suction stroke of piston 16 and is forced through'discharge ball'check valve 18 to and through g'the high pressure pump outlet 20 into the high pressure inlet passage or chamber 22 0f the valve A valve assembly .such as that knownas a Gaulin Single pressure sources. 7

An aqueous slurry isparticularly suitable because of the low cost and availability of water and because theIusual steps employed in removing non-micaceous minerals from However; any liquid which does not detrimentally aifect the mica can be used.

The invention will be more clearly understood from the following description in conjunction with the accompanying drawings, inwhich:

assembly 23 and against valve 24 which is urged toward valve seat 126. by'a heavy spring 33. The high pressure exerted on the valve 24 by the. slurry in the confined passage 22' forces the valve slightly away (a fraction of an inch) :from itsseat 26," whereby the slurry under pressure flows at an extremely high velocity through the highly restricted valve opening28 against an annular impact ring 39. extendingfiaround the valve. The slurry then flows throughthenarrow passagei29. between the ring 30 and the adjacent outer peripheral walls of the valve and seat. Delaminati'on and grinding are achieved by the shearing effect on the mica particles of the closely spaced valve seat 2f6and' valve face 31' forming opening 28 and of the closely spaced impact ring and outer peripheries of the valve and valve: seat forming passage 29, all of which I are 'made of a very hard material such as tungsten carbide,

FIG. 1 is a flowdiagram of the method of the present.

invention with the various units designated as boxes. 7

parts of the abrasive action of the mica slurryafter the valve assemblyhas been in use for some time.

FIG. '8- is a'view taken along the line 8-8 of FIG. 7. FIG. 9 is a view taken along the line 9-3 of FIG. 7. 'FIG. '10 is a section in elevation of another embodiby the turbulence and cavitation'of the mica particles as they'flow through opening'28 against impact ring 30xand through passage 29 and by shattering and impact of the particles against' the .impactring 3t) and valve face 31. The variouschangesfiin direction of flow of the slurry from 22 tof23'and from 28' to 29 also contribute to the delaminating and grinding phenomena. It is believed thatthe liquid media contributes to. the effectiveness of the FIG. 2 is a flow diagram corresponding to FIG. 1 but planar-surfacesthereof aligned in the direction of flow through the] opening so that they are discharged from the ment of a valve assemblyv for carrying out the method of thepresent invention and having a mechanism for rotating the valve surface with whichthemica slurry comes in:

contact tofreduce harmful Wear effects'of the slurry onthe valve and valve seat. i I I Before explaining i-n detailv the present invention. it is application to the details and arrangements illustrated and described herein, sincethe invention iscapable of other embodiments and of being practiced or carried out to be understood that the invention is not limitedin its in various ways. Also, theiterminology"employed and the theories, described herein-areffor the purposes of description andexplanation andnot of limitation audit is i;

not intended to limit the inventionjclaimedj'herein beyond pegmatite or Queue-Le; other mica deposits) is first" crushedinto' small particles in a conventional. ore crushremaining non-micaceous minerals are then removed tea a the mica in a conventional froth'flotationunit or other micaconcentrator utilizing water. and suitableflotation sembly 23. shown in the drawings, the 'diameter a' (see opening-and hit the impact ring 'edgewise. This belief is supported by the fact that initially with a new impact ring the impact surface immediately opposite the dischargeof the opening-developsa very finely etched hair-line groove and by the fact that the postage stamp-shaped mica particles in the finished product have two dimensions (planar dimensions) Whicharegreater than the size d of the opening and the width of the hair-linegroove. a 1

The slurry containing the"delaminated' ground mica Zfiows from pressure pum'p and valve assembly 12 to a second pressure-pump and valve assembly 32 of the same ,construction as 12 and in [which the "*mica is further 'delarninated' and ground, The delaminated mica flows from 32 to a. conventional. screen or classifier 34 in which the mica particles whichfare coarser than desired in the T final endflproductam removed. The second pump; and "valve as'sembIyESZjpanbe omitted in which case the'mica slurry flows from, :12 directly to '34. The' micaslurry containing fine mica flakes flOWS fIOIl1;34H tO iaconventional centrifuge'36' where the .bullc 'of the water is removed' and maybe recycledback to th' V a "slurry feed tank 4. The'mica particles are, then dried a conventional dryer 38' andvtheadried mica is passedjtoa conventional 'deagglomerator ifiinwhich any agglomerates formed during centrifuging. and drying are broken up; The finished "product discharged; from the; deagglorneratorj 40- and comprises fine 'micaflake's- .ofl p a bulk density and top quality.y

The fio w. described above is c ontinuousandfihedelaminationandgrinding ofthe mica' occursinstantaneously as it .passes through aperturelzg;'strikesi ring. 30 and passes through passage zi In the particular valve as- 13 FIG. 4) of the bore forming valve inlet 22 is 0.1877 inch, the diameter 12 of the valve 24 is 0.375 inch, the distance between the impact ring 30 and the outer peripheral surfaces of the valve 24 and seat 26 is .032 inch, the distance d between the valve face 31 and the valve seat 26 (width of opening 28) is between .001 and .005 inch, the width e of impact ring 30 is .2848 inch and the thickness f of valve seat 26 (distance of travel of slurry while between the valve and seat) is .0935 inch. The spring 33 is of sufficient weight and is compressed suficiently to exert, when flow through the assembly is 0, a closing force on the valve which is slightly less than the force exerted on the valve by the liquid slurry which is under a pressure of about 6,000 pounds per square inch so that, during flow of slurry through the valve assembly, the valve 24 is forced a fraction of an inch away from the seat 26 by a slight compression of spring 33 to form the annular opening 28 through which the slurry flows at a velocity of about 540 feet per second from high pressure area 22 to the low pressure (substantially atmospheric) area outside the valve. The above-mentioned specific dimensions, pressure and velocity are given by Way of example only and it is not intended that the invention be limited thereto.

It is advantageous to recycle the coarse mica particles separated from the fines at screen 34 from the screen back to the slurry feed tank 4 as shown in FIG. 2.

The slurry feed tank 4 can be any tank fitted with an agitator designed to keep the mica books in uniform suspension. The screen or classifier 34 can be any of a variety of rotating or vibrating screens capable of handling slurries or any other type of wet classifier such as a rake classifier. The centrifuge as can be a perforate bowl type fitted with a suitable filter media or a solid bowl type. The dryer 38 can be of conventional design for removal of water from the centrifuge cake. The deagglomerator 40 can be any kind of device, such as a hammer mill, which will break up the dried mica. This mica sometimes cakes into hard lumps as it passes through the dryer and normally needs only a slight impact to reduce the lumps and restore the mica to loose particles. Although an annular valve opening 28 is shown in the drawings and is preferred, a fixed or adjustable aperture of any kind and shape can be used in conjunction with an impact surface in front of the aperture discharge.

As indicated above, the individual sheets of mica within the books are separated and reduced to fine particle size by shearing, turbulence, shattering, impact and cavitation forces as the slurry of books is forced under pressure through the restricted opening 28 of the valve at extremely high velocities and is impacted against the ring 30 and flows through passage 29. The effectiveness of this phenomenon in producing fine, flaky, platelike particles has been found to depend on the following variables:

N0. Variable l. CONCENTRATION Holding the other variables constant, the lower the concentration of mica books in the slurry, the lower the bulk density of the resulting product. The concentration can be as high as can be handled in the pressure producing device so long as the slurry is flowable and can be as low as is desired. By flowable it is meant that a mass of the slurry will change its shape under the influence of gravity when the mass is initially placed on a stationary horizontal surface. Concentrations from /2. percent to 50 percent have been used, but 1 percent to 2. PARTICLE SIZE RANGE OR AVERAGE PARTICLE SIZE Holding the other variables constant, the larger the av erage particle size, the lower the bulk density of the resulting product. While an absence of exceedingly fine books has been found to give a better product, the method of the present invention can be used no matter how fine the average particle size may be by adjusting the concentration downward (see Example 1 below and discussion of Variable No. 1 above) and by recycling the coarser particles removed at screen 34 (see Example 5 and discussion of Variable No. 5 below). Particles are limited in maximum size only by the capabilities of the pumping or pressure producing device and the internal dimensions of the valve, particularly, between the valve face 31 and the valve seat face 26. To this extent, the particles in the feed may be considered as being sized particles, i.e. they are not substantially greater in size than the abovementioned maximum size which can be handled by the valve without plugging it to thereby render it inoperative. In practice, a particle just passing a 20 mesh screen can be easily handled. If a piston pump is used, the larger the pump, the larger the particles which can be handled. The eifect of varying particle size is demonstrated by Example 2 below.

3. SLURRY PRESSURE Holding the other variables constant, the higher the slurry pressure, the lower the bulk density of the resulting product. Pressures as high as 12,000 pounds per square inch have been used successfully. The maximum pressure is dictated only by the limitations and capabilities of currently available equipment. Some pumps presently available can develop 20,000 pounds per square inch and higher. As a practical matter, the upper limit is consistent with good product quality without undue equipment main tenance and wear and the lower limit is not the lowest pressure at which the phenomenon can be detected, but

rather represents a point below which other variables must be adjusted to such a point as to make the process lose its commercial advantage. About 250 pounds per square inch may be considered as a practical lower limit, although with certain soft mica deposits some delamination may occur at pressures as low as about pounds per square inch. Originally, pressures from about 1,500 pounds per square inch to 6,000 pounds per square inch were studied and more recently, pressures from about 500 and 600 pounds per square inch to 6,000 pounds per square inch have been used successfully and are presently the most practical. All pressures referred to hereinbefore and hereinafter are gage pressures. The efiect of varying pressure is demonstrated by Example 3 below.

4. NUMBER OF PASSES Holding all other variables constant, the greater the number of passes, the lower the bulk density of the resulting product. The effect of increasing the number of passes is demonstrated by Example 4 below.

5. REMOVAL OF FINE PARTICLES AND RECYCLING COARSER PARTICLES It has been found that by passing the slurry through the valve, removing the desired fine mica flakes by wet screening or the like, recycling the oversize material and adding raw mica and water to restore the concentration,

i The smaller it is, the better theresults. the large enough to accommodate the discharge from, opening v28. The delaminating effects decreases, rapidly at distances greater than about 0.25 inch. Adistance c of less than -about'.0.10 inch is preferred.

"Schis't located in Chester,Vermont.:

. Y 7 7 g lower limit is dictated onlyfby practical considerations. Opening sizes greater than about .090 inch require such a high pumping rate or such a small dimension a (FIG.

4) to achieve adequate velocities through opening 28 that they are not commercially practical. In fact, opening; sizes greater than about ,O50'inch areydifficult to use,

although with certain soft mica deposits and under .cer-:

.tain conditions, some delaminationmay occur with open-v -ing sizes as large as about 0.10 inch.

The-velocity of the'slurry through the opening 28 depends onthe size of the opening, the fluid pressure, the force exerted by thespring 33, the capacity of thepump volumetric delivery) and the. magnitude of dimension a. Velocities in the nature of about 540 feet per second and greater, including sonic velocities, can be used. Maximum velocities are dictated only bypract'ical, ,considerations and limitations of available equipment. Velocities between about 300-feet per second and 1,000 feet per second-are preferred. With most mica concentrates, the

delaminating phenomena decreases rapidly below about.

250 feet per second, although with certain soft mica de'.

posits, delamination may occur at velocities as low as 'opening'28 becomes more restricted and the slurry velocity increases. The maximum spring force is dictated by maximum pressures and velocities which in turn are dictated "by .limitations of currently available equipment. The minimum spring force is dictated'only by the mini num pressures, velocitiesand valve opening sizes at which substantial delamination occurs.

Although a spring 33 is shown urging the valve 24 .toward closed position, any other resilient, yieldable :means can be used such as a pneumatic or hydraulic motor ,or block-of elastic material such as a hard rubber material.

The-distance c of the impact ring 30 fromthe adjacent i peripheral surfaces'of the valve and seat is important. However, it must Examples The range of 'efiiciencies and performance which can be obtained by varying the above Variables 1' -to 5 are mani- V V V 1 8 V In each example, the whole or a fraction (as indicated) of the mica discharged from froth flotation'apparatus' 3 was passed to 4 where an aqueous slurry of properconcentration (as indicated in theexamples) was made and then flowed through the variousunits asdescribed above and shown in flow diagrams l and 2. In. Examples 1 to 4, How was'according to'FlG. 1 except. that in run 1 of Example 4 the .pressure'purnpand valve assembly, 32 was omitted. In Example 5, steps 2 ted, the flow was according to FIG. 2, whereas instep 1 the flowwas according to FIG.'1 with the exception that +325 mesh particles separated from the slurry in 34 were recycled from 34 to 4. In Example 6, flow was according to FIG. .1.

' EXAMPLE 1.'-EFFECT .OF .VARYIVNG. CONCENTRATION.

OF SLURRY mica concentrate Concentration Bulk density of of mica in'water n1inus825 mesh 'Ruii No.

slurry, percent traction,-lbs.lcu.

by weight It.', removed from 40 nxalxr LE er -EFFECT OF VARYING AVERAGE vPARTICLE SIZE OF MICA FEED 7 Pressure in 12 and 32': 6,000 pounds per square inch Number of passes: 2 Y

Removal of fine particles between passes: None Concentration: 10% by Weight Same rate of slurry feed as Example 1 p Bulk;density of minus 325 mesh 7 Run No. Feed description fraction,lbs./cu.

: it.,- removed 1 Fractionof mica concentrate discharged l6. 4

' from 3, minus 100 mesh only.

2 Fraction of, mica; concentrate discharged 12.1

' from 3, plus 100 mesh only.

. EXAMPLE summer OF :V-ARYINGY PRESSURE IN 1 1211111332 1 Feedt' Schist mica concentrate as discharged 'ffi'ommica. confold. The following examples are meant tosupport the I preceding statements and in no way are. intended to limit the scope of the invention.

The mica feed for the followingexamples, with the' exception of Example 6, 'wasobtained from the Gassetts The schist was.

The

crushed and ground in 1 to pass a 20 mesh screen.

garnets and heavy minerals were removedin 2. The mica wasse'parated from silicav and other non-micaceous.

'niinerals 'byfroth 'fiotat i'on in 3; I Aparticle, size analysis I of the resulting mica Mesh:

concentrate is as follows: v v Percent I Minus 20plus 30 0.62

Mlmls 'P i a a of Minus 00 Minus .60'plus'- 10 0 .Run'Nm. Numberof .rt/tesh Fr'ac- Minus, plus 200 V i Passes I 153311383 Minus 200 plus 325.. I p y from 40, 'Minus325'on pan s, 114.0

i w i A .1 20.3 2 15.8

' 1 Bulk densityi 48 52.1bs. per-cu. ft.

. centrator 3 I Rate of slurry feed Same as Example 1 Number of passes :2

Removaloffine particles between passes :None.

'Qo'n'centration 5%.by weight Bulk Density 7 .Pressure of MinnsGO Run No; Lbs/Sq. Y Mesh Frac- I 7 Inch' tion, Lbs'J/Cu.

It, Removed from 40 1 EXAMPLE 4. EFFECT OF vARYINs NUMBER on PASSES' a Feed: Schist mica concentrate asdischarged from mica con centrato1'3 i Rate ofislurry feed: Sameas Example 1 ,Removalof fine particles between passes: None "Concentration 5% by weight Pressure: 6,000. p0unds per'squai' inch Bulk Density EXAMPLE 5.REMOVAL OF FINE PARTICLES (325 MESH) WVIlH RECYCLING OF COARSER PARTICLES 325 MESH) Feed: Schist concentrate as discharged from mica concentraor Rate of slurry feed Same as Example 1 Concentration by weight Pressure 6,000 pounds per square inch Bu k Density Norn.Conversion of approximately of total material handled per pass to -325 mesh low density mica is obtained after stabilization.

The initial 200 parts of feed to 12 was all raw feed. 133.5 parts of the discharge from 32 was 325 mesh and continued on to 40. 66.5 parts were +325 mesh and were recycled back to 4 and 133.5 parts of raw feed were added to bring the total feed back to 200 parts. Sufficient water was added to provide a 20% concentration. The neew feed was fed to 12 and then directly to 34 as shown in FIG. 2. 62.3 parts were -325 mesh and were passed on to 40. 137 parts were +325 mesh and were recycled. This increase in the amount of +325 mesh discharged from 12 was due to the fact that only one pass was used in step 2 and the fact that the new feed with the recycled mica contained more coarse particles than the original feed. 62.3 parts of raw feed were added to the recycled feed to bring the total back to 200 parts and enough water was added to obtain a 20% by weight concentration and the new feed of step No. 3 was fed to 12. Thereafter, the amount of -325 mesh particles produced stayed at about 25% of the feed and the amount of recycled +325 mesh particles stayed at about 75% of the total feed. Thus, conditions became stabilized after the first step and bulk densities of between 12 and 13 pounds per cubic foot were continuously obtained (discharged from from raw feed having a bulk density of 4852 pounds per cubic foot continuously fed to 4.

EXAMPLE 6 A sample of conventional mica scrap (not schist) having a particle size analysis as follows was used in another run (fed to 4) under the following conditions:

1 Bulk density: 20.0 lbs/cu. ft.

Rate of aqueous slurry feed: Same as in Example 1 Pressure in 32: 6,000 pounds per square inch Pressure in 12: 2,000 pounds per square inch Number of passes: 2 (12 and 32) Removal of fine particles between passes: None Concentration: 10% by weight in water Bulk density of minus 325 mesh fraction removed from 40: 9.55 lbs/cu. ft.

Percent converted to +325 mesh: 38.6%

In accordance with the present invention, mica having bulk densities less than about 7 or 8 pounds per cubic foot and as low as about 3 and 4 pounds per cubic foot and having a fineness of much less than 325 mesh can be produced efficiently, economically and continuously.

. "i0 Mica having such low bulk densities has never before been produced.

Densities of about 3 and 4 pounds per cubic foot were obtained with the use of the conditions of Example 1 but with 4 passes, a rate of slurry feed to 12 of 120 gallons per hour, a fluid pressure of 3000 pounds per square inch and a concentration of 1% and with a North Carolina mics scrap having the following particle size analysis as feed:

Mesh: Percent Plus 20 mesh 1.5 Minus 20 plus 30 3.3 Minus 30 plus 40 1 8.1 Minus 40 plus 60 23.0 Minus 60 plus 100 26.8 Minus 100 37.3

1 Initial bulk density 28-30 lbs. per cut. ft.

The abrasive action of the mica slurry on the surfaces 26 and 31 of the valve seat and valve respectively, produces the following wear el'rects on such surfaces after the valve assembly has been operated for a period of time.

Referring to FIGS. 7 and 8, at the ring shaped area 34 on the valve face 31 where the mica slurry changes direction and is simultaneously accelerated by the decreased cross sectional area as it enters the restricted opening 23, a ring shaped area of wear 34 slowly develops. This ring shaped area develops into a ring shaped groove 34 which destroys or alters the working surface 31 of the valve and thereby prevents the achievement of a proper uniform clearance d between the surfaces 26 and 31. As a result the quality and uniformity of the resulting delatninated mica deteriorates. Simultaneously as the ring shaped groove 34 develops on valve face 31 an area of wear develops on the valve seat surface 26. This area of wear is either in the form of a fine line 35 or wide channel .36, as shown in FIG. 9. The former is typical of softer valve material; the latter is typical of harder valve material such as tungsten carbide. The mica slurry flow tends to channel through these channular areas of wear 35 and 36, thereby reducing velocity and shear effects on the mica particles and making pressure control and the achievement of proper slurry velocities diflicult or impossible. This prevents proper delamination and grinding and consequently causes the quality and uniformity of the resulting delaminated mica to deteriorate.

To remedy these wear effects, it is necessary to remove the valve seat 26 and valve 24 from the valve assembly 23 and have the surfaces 26 and 31 relapped and polished by conventional machine shop practice.

It has been found that the formation of channels 35 and 36 can be substantially reduced or eliminated and that the groove 34 will develop more uniformly by rotating the valve about its longitudinal axis.

A. device in which the valve is so rotated and which is sufiiciently rugged in design to operate satisfactorily at production rates of several tons per hour of fine, delaminatcd mica from a coarse and abrasive mineral slurry, is shown in FIG. 10. The valve 37 has the same cross sectional shape and dimension as valve 24 in FIGS. 3 to 6 and is rotated by a rotating shaft 38 to one end of which the valve 37 is anchored by means of a press or interference iii of the end of the valve in a recess in the end of the shaft.

The shaft 38 is supported by two radial package type bearings 41 and 42 equipped with dust and grease seals and enters the fluid chamber 43 through a stuffing box 44. The radial bearings 41 and 42 are press fitted into the radial bearing supports 45 and 46. The stufiing box 44 the stationary spring 60.

Rotating motion is imparted to the shaft 33 by; means of a'p'ulley 54) which isvkeyed to the shaft 38. The

pulley 59 is driven by a motor '51, pulley 52 and v belt 53.

The cylindrical valve seat 39 has the same cross sectional shape and dimensions asvalve seat 26 in FIGS. 3

to 6 and issupported in position by. a cylindrical valve seat holder 46 into which an end thereof is anchored by I means of a press or interference fit. H

40 is supportedin an aperture in the. end wall'ifi of, fluid Valve seat holder chamber 43. The valve seat 39. and valve seat holder are hollow and haveaxially aligned internal bores 39a and 40a. respectively whichhave. the same cross sectional shape and internal diameteras high pressure inlet passage or chamber. 22 in FIGS. 3, to 6 and into which mica slurry under pressure is pumped from pump it). r

The impact ring 54 has the same shape and dimensions as impact ring 30 in FIGS. 3 to 6 and isheld by means of a press fit in the impact ring holder 55' which'in turn .is supported and properly positioned by a wall 56, which is supported by the wall 69 of chamber 43' The pe ripheral portion ofwall 56 adjacent outlet 6230f the chamber 43 is bevelled at 43a to permit the, mica'slurry tofloW from the chamber 43 on both sides of Wall56 into out-' let68.. 7 7 I The valve- 37 is urged axially toward the valve. seat surface 67 of valve seat 39 by the action of a compres-b sionspring 60 acting on the. end of shaft 38 in-an axial direction through a thrust bearing assembly 61. The

thrust bearing assembly 61 permits the shaft 38 to rotate while being urged to the left, as shown in FIG-10, by

.Thrust bearing assembly 61 comprises a plate 61a which is urged to the left as viewed in FIG. 10 by spring .60. Plate 61a acts on plate 61b through ball bearings 61c and through the engagement of plate 61a with hub- 61d of plate 61b to urge plate 61b to the left; Plate 61b acts on shaft 38 to urge it to the left through ball bearings 61c and plate 61faflixed1to the end of the. shaft. The plates and ball bearings of thrust. bearing assembly 61 are housed withina free floating housing 61g which is prevented from rotation but which is free to move longitudinally. Any conventional thrust bearing assembly can be used.

The amount of force delivered by the spring 60 can be 7 adjusted by means of compression adjustment ,plug' 62.

The plug 62 is threaded in a supporting Wall 63 and has in the otherz'direc'tion so that it moves axially to'the right decreases the spring force exerted-on the valve 37'; Con- J tinned movement to the right of plug 62 is finally transferred through nut'65 and the spring'rod '64 to plate 61b.

force on the valve37 so that the unit to release the spring can be disassembled.

Y Theslight axial movement at shaft 38 and valve 37. I between closed position "of thefvalveand maximum open Y :position is notenough to interfere ,Wlthftht'i pulley drive 50, 52 and 53;,

The parts of the-valve assembly subject to the. most severe conditions, re. the valve 3 7, the valveseat 39, and

the impact ring 54,'are best made of the hardest obtainable materials suchas tungsten carbide. Because of the high cost of these materials, the apparatus shown in FIG;

and can be replacedif'necessaryi.

.10 is designed'so thatdhe's'e parts are of minimumjsize The dimensions a, b,j c, d, e,- and f in the valve assembly of FIG. '10 are} substantially the same as the correspond-- l2 The rotating motion of the valve surface 66 with respect to both the valveseat surface 67 and'the' impact surface of impact ring 54 causes the slurryv therebetween to impact a constant lapping and'polishing action on such 5 surfaces which prevents the formation of chan'nels35, 36 in surface 67 as shown inFIG; 9. The surface 67 and the portion of surface 66 facing surface-67 wear uniformly and the equipment can be operated until the V, groove :34 (FIG. 8,)" becomes sodeepas to. cause striking a of the ungrooyed peripheral portion of surface, 66 against surface 67. When-thesurfaces begin to strike, the valve can be disassembled and'the surfaces 66 and 67 can be relappedarid polished by conventional machine shop practice. a j

Valve 37 can be. rotated as slowly as 0.5 revolution [per minute '(r.p.rn.) and as fast as"3540'r.p.-m; or more. Speeds of conventional motors, as for example 1750 r.p.m., are satisfactory, However, 600800 r.p.-m. is a preferred range andcanrbe achieved through the proper selection of motor 51 and the'pulleys 50 and 52.

The rotary motion imparted to valve face 66 may be oscillatory. r I 1 Y I Flow through the valve assembly of FIG. 10 should be adequate to assure a layer of slurry between the surfaces 66 and 67, which layer of .slurry provides a constant lapping action. on the surfaces; and prevents-the surfaces-from rubbing .iagainstyfgeach other. ,Forexample, with a valve seat 39 having an internal diameter a'of 0.250 inch a flow of about four, gallons per minute (g.p.rn.) or fniore' is adequate.

The fluid chamber-43 cani'beformed by a cylindrical wall .69 ora series of flatwalls such as a -box,',and is I closed at the .ends' by plate or ,walll70, which supports the valve seat'holder40', and the .s tufiing box 44.

Withreference to FIG. 10,'rnineral slurry-under pressure from the. pump 10 passes through the bores'40a and -39a in the valve seat holder and valve seat'39 respectively againstthe' rotating valves37 to'force surface 66 away from surface 67 againstfiheforce exerted on the 40 valve by spring 60, to thereby provide restricted opening d between surfaces 66 and 67 through which opening the slurryfiows at a high velocityi'a'gainst the impact ring 54, into fluid chamber .43 and out-"of the fluid chamber 43 through outlet 68 to another pump and valve assembly or 45, to the classifier 34. w

' "The method of the present inventionl c'an befused to delarninate and grind any mineral which occurs: in'the .formof laminated layers such as'se'ricite,t'alc and other jso-called platy minerals. The word mica as used-herein includes sericite. See A" Glossary of the Mining and Mineral IndustryjbyA-l-bertH. Lay, Department of the .Iriterior 'Bulletin 95,"page 603. 1 Talc *havinga bulk rdensityof 15 pounds per cubic, foot and Jess; 'i.e. as low as six'poundsfper cubic foot, has been produced" with the 'use of the-method of the present invention. 7

V Althoughin the above-described method the rnica'slurry "discharged from the valve opening is directed against an impact surface, with certain soft deposits of mica and talcfthe impact .ring can be omitted, in which case, de-

laminaticn'is accomplished by passage through the valve opening only," i a I This applicationfis a continuation of ourfapplications Serial Nos. 197,813 and*1'97,81-2, both filed May 17, 1962,

' 55 and both now'iabandoned. Thisapplication discloses only I subject niatter'disclosed in said application Serial No.

197,813, which is agcontinuationof application Serial No.

1,189,933, filed April 24, l 962,,n0 w abandoned, which in turn is a; continuation of our applicatiorrjserial No. 782 7 992 jfile'd. December 22', 1958,1i1ow abandonedwhich is "-inturn*a continuation-in-part of our, application Serial No;,758',930,ffiled September 4, "1958; now abandoned. claimr. 1

lfA 'rn ethod of delaminatingi siz ed laminar, mineral v aarticles selected from the group consistingof mica particles and talc particles, said method comprising forcing a fiowable liquid slurry of said mineral particles in the form of a thin film edgewise through a thin, hard surfaced gap under a high pressure of at least 250 pounds per square inch and at an extremely high velocity by virtue of reduction of said higher pressure to a substantially lower pressure to separate the layers of said laminar mineral particles.

2. A method according to claim 1, said pressure forcing said gap to open to provide said flow of slurry therethrough against a yieldable force tending to close said gap.

3. A method according to claim 2, the major portion of said particles having a particle size greater than about 200 mesh.

4. A method according to claim 2, said film having a maximum thickness of about 0.09 inch and moving through said gap in a direction at an angle to the direction of flow to the gap, said pressure being at least about 600 pounds per square inch.

5. A method of delaminating sized laminar, mineral particles selected from the group consisting of mica particles and talc particles to reduce the bulk density thereof, said method comprising forcing a flowable liquid slurry of said mineral particles in the form of a thin film edgewise through a thin, hard surfaced gap under a high pressure of at least 250 pounds per square inch and at an extremely high velocity by virtue of reduction of said higher pressure to a substantially lower pressure against a hard impact surface to separate the layers of said laminar mineral particles and reduce the bulk density thereof.

6. A method of delaminating sized laminar mica mineral particles, said method comprising forcing a flowable liquid slurry of said mica mineral particles in the form of a thin film edgewise through a thin, hard surfaced gap under a high pressure of at least 250 pounds per square 14 inch and at an extremely high velocity by virtue of reduction of said high pressure to a substantially lower pressure against a hard impact surface to separate the layers of said laminar mica mineral particles.

7. A method according to claim 6, the major portion of said particles having a particle size greater than about 200 mesh.

8. A method according to claim 6, said film having a maximum thickness of about 0.09 inch and moving through said gap in a direction at an angle to the direction of flow to the gap, said pressure being at least about 600 pounds per square inch.

9. A method according to claim 6, said slurry being an aqueous slurry.

10. A method according to claim 6, said pressure forcing said gap to open to provide said flow of slurry therethrough against a yieldable force tending to close said gap.

11. A method according to claim 10, the major portion of said particles having a particle size greater than about 200 mesh.

12. A method according to claim 10, said slurry being an aqueous slurry.

13. A method according to claim 10, said film having a maximum thickness of about 0.09 inch and moving through said gap in a direction at an angle to the direction of flow to the gap, said pressure being at least about 600 pounds per square inch.

References Cited in the file of this patent UNITED STATES PATENTS 1,654,268 Nielsen Dec. 27, 1927 1,739,360 Hopkins Dec. 10, 1929 1,934,637 Rafton Nov. 7, 1933 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,162, 379 December 22, 1964 Morris I. Cohn et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 15, for "any" read and column 2, line 17, for "10-14" read (10-14 column 7, line 47, for "effects" read effect same column 7, in the table, lines 65 to 75, for 19.0" read 19.0 and Bulk" read Bulk column 9 line 26, for "neew" read new same column 9 in the table, lines 50 to 60 for 44.0" read 44.0 and Bulk" read Bulk column 10, 'in the table, lines 10 to 20 for 8.1" read 8.1 and lnitial" read Initial (SEAL) Signed and sealed this 3rd day of August 1965 Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Altvsting Officer Commissioner of Patents 

1. A METHOD OF DELAMINATING SIZED LAMINAR, MINERAL PARTICLES SELECTED FROM THE GROUP CONSISTING OF MICA PARTICLES AND TALC PARTICLES, SAID METHOD COMPRISING FORCING A FLOWABLE LIQUID SLURRY OF SAID MINERAL PARTICLES IN THE FORM OF A THIN FILM EDGEWISE THROUGH A THIN, HARD SURFACED GAP UNDER A HIGH PRESSURE OF AT LEAST 250 POUNDS PER SQUARE INCH AND AT AN EXTREMELY HIGH VELOCITY BY VIRTUE OF REDUCTION OF SAID HIGHER PRESSURE TO A SUBSTANTIALLY LOWER PRESSURE TO SEPARATE THE LAYERS OF SAID LAMINAR MINERAL PARTICLES. 